In integrated circuit production, a layer-to-layer alignment and registration of fabrication masks is critical. The alignment of one mask layer to another or of a mask layer to a previously applied dopant is frequently critical to the fabrication of active devices or to electrical properties such as isolation capabilities, threshold parameters, or breakdown voltages. A misalignment of a sequence of fabrication steps may mean that a device is out of specification or inoperable. Yield and performance numbers for a device in production may vary significantly causing considerable cost consequences.
Typically a device site on a semiconductor wafer will have alignment or registration marks in the kerf or scribe line area. These registration marks allow automated or manually adjusted optical equipment, such as mask alignment tools, to register a mask layer to the die site. Many interdependencies exist in mask alignment including a lack of “run-out” (nonlinearity) in the features across the mask surface as well as an accurate planarity of the mask relative to the die surface. Variation of these quantities must be kept to a minimum over a considerable distance in order for features in the middle of the die area to be rendered accurately.
Certain technologies require device dimensions to be critically positioned in order to meet specifications and perform as intended. Device performance parameters such as breakdown voltages, threshold voltages, and electrical isolation capabilities depend critically on fabrication layer-to-layer registration in certain integrated circuit technologies such as high-voltage MOS (HVMOS), DMOS and BCDMOS (Bipolar CMOS-DMOS). These technologies rely crucially on fabrication alignment to have sufficient electrical performance characteristics and yield.
For example, in DMOS technology, a drain-to-source breakdown voltage (BVDSS) and an “on-channel resistance” (RDS(ON)) vary directly with a variation in layer-to-layer registration. What is needed is a method and structure to allow mask alignment and registration of the critical layers to be accomplished within either a die site frame or a die site itself.